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The C and C++ Include Header Files

cat -n /usr/include/stdc-predef.h

     1	/* Copyright (C) 1991-2026 Free Software Foundation, Inc.
     2	   This file is part of the GNU C Library.
     3	
     4	   The GNU C Library is free software; you can redistribute it and/or
     5	   modify it under the terms of the GNU Lesser General Public
     6	   License as published by the Free Software Foundation; either
     7	   version 2.1 of the License, or (at your option) any later version.
     8	
     9	   The GNU C Library is distributed in the hope that it will be useful,
    10	   but WITHOUT ANY WARRANTY; without even the implied warranty of
    11	   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    12	   Lesser General Public License for more details.
    13	
    14	   You should have received a copy of the GNU Lesser General Public
    15	   License along with the GNU C Library; if not, see
    16	   <https://www.gnu.org/licenses/>.  */
    17	
    18	#ifndef	_STDC_PREDEF_H
    19	#define	_STDC_PREDEF_H	1
    20	
    21	/* This header is separate from features.h so that the compiler can
    22	   include it implicitly at the start of every compilation.  It must
    23	   not itself include <features.h> or any other header that includes
    24	   <features.h> because the implicit include comes before any feature
    25	   test macros that may be defined in a source file before it first
    26	   explicitly includes a system header.  GCC knows the name of this
    27	   header in order to preinclude it.  */
    28	
    29	/* glibc's intent is to support the IEC 559 math functionality, real
    30	   and complex.  If the GCC (4.9 and later) predefined macros
    31	   specifying compiler intent are available, use them to determine
    32	   whether the overall intent is to support these features; otherwise,
    33	   presume an older compiler has intent to support these features and
    34	   define these macros by default.  */
    35	
    36	#ifdef __GCC_IEC_559
    37	# if __GCC_IEC_559 > 0
    38	#  define __STDC_IEC_559__		1
    39	#  define __STDC_IEC_60559_BFP__ 	201404L
    40	# endif
    41	#else
    42	# define __STDC_IEC_559__		1
    43	# define __STDC_IEC_60559_BFP__ 	201404L
    44	#endif
    45	
    46	#ifdef __GCC_IEC_559_COMPLEX
    47	# if __GCC_IEC_559_COMPLEX > 0
    48	#  define __STDC_IEC_559_COMPLEX__	1
    49	#  define __STDC_IEC_60559_COMPLEX__	201404L
    50	# endif
    51	#else
    52	# define __STDC_IEC_559_COMPLEX__	1
    53	# define __STDC_IEC_60559_COMPLEX__	201404L
    54	#endif
    55	
    56	/* wchar_t uses Unicode 10.0.0.  Version 10.0 of the Unicode Standard is
    57	   synchronized with ISO/IEC 10646:2017, fifth edition, plus
    58	   the following additions from Amendment 1 to the fifth edition:
    59	   - 56 emoji characters
    60	   - 285 hentaigana
    61	   - 3 additional Zanabazar Square characters */
    62	#define __STDC_ISO_10646__		201706L
    63	
    64	#endif